1. Field of the Invention
This invention relates to battery chargers and, more particularly, to apparatus for charging a battery and for a end to a method of charging a rechargeable lead acid battery.
2. Description of the Prior Art
Battery charger apparatus of the prior art typically includes a transformer for decreasing line voltage to a desired level and a rectifier for changing alternating current to direct current. The direct current is applied across the battery to recharge the battery. There have been variations of the relatively simple battery charging apparatus described in the previous sentence, but typically the primary differences between various types of battery chargers is simply in the amount of current applied to the battery being charged.
An inherent problem with applying a relatively high charging current is in the amount of heat generated. The heat generated has a deleterious effect on the battery being charged.
Pulse charging was used at least as early as the 1950s for charging NiCd (nickel cadmium) aircraft batteries, but was not adapted to lead acid batteries.
There are basically two ways of charging a battery, one way is to utilized a relatively low charging current for a relatively long period of time, and the second way is to utilized a relatively high charging current for a relatively short period of time. In the latter case, the heat buildup is a prime consideration. On the other hand, if charging time is unimportant, then the utilization of a relatively low charging current is preferable because the heat problem is obviated.
The apparatus of the present invention overcomes the heat problem and also overcomes the time problem by providing a charging circuit in which a charging current is supplied for a period of time, then a discharge resistance is placed across the battery for a short period of time, followed by a sampling of the current in the battery. Logic is utilized to control the charging time, the discharging time, and the sampling or sensing of the battery being charged. The charging current is varied in accordance with predetermined parameters so as to maximize the charging current, and accordingly minimize the charging time, while at the same time substantially eliminating the problem of heat buildup.
U.S Pat. No. 3,597,673 (Burkett et al) discloses a battery charger apparatus which utilizes pulse charging. Discharge pulses are disposed between charge pulses. After a predetermined battery terminal voltage is achieved during charging, the charging current is reduced to a trickle. Specific circuitry is disclosed.
U.S. Pat. No. 4,829,225 (Podrazhansky & Popp) discloses another battery charging apparatus. Different embodiments are disclosed. Pulse charging is again involved. After a charging pulse, a depolarization pulse is used to discharge the battery across a load. The battery condition is sampled during the depolarization pulse. The depolarization pulse time is followed by a stabilization period, and then the sequence is repeated until the battery is charged to the desired level. The depolarization pulse is not specifically explained. Examples of using the apparatus of the '225 patent with different types of batteries is disclosed. For example, an example is given for charging a 9 volt alkaline battery, nickel-cadmium batteries, and a 12 volt automobile battery.